A student went on a five-minute stabbing spree at a Pennsylvania high school this morning, wounding at least 22 people and leaving two critically injured and fighting for their lives.

Alex Hribal, a 16-year-old sophomore at Franklin Regional High School in Murrysville, Pa., used two 8-to-10 inch "kitchen-type" "straight" knives in the attack, which started shortly after 7 a.m., police said.

Authorities said Hribal would be charged as an adult with four counts of attempted criminal homicide, 21 counts of aggravated assault and one count of possession of weapons on school property. He was being held without bail in a juvenile detention center in Westmoreland County.

After the spree began, the school resource officer stationed at the school, William "Buzz" Yakshe, used his radio to alert police, telling them of a critical incident unfolding at the school, according to Murrysville Police Chief Thomas Seefeld.

"When we got there we saw a hallway in chaos, as you can imagine," Seefeld said at a press conference this afternoon. "There was a lot of evidence of blood on the floors and in the hallway, we had students running about, trying to get out of the area."

Franklin Assistant Principal Sam King tackled the suspect during the attack, and was joined by Principal Joan Mellon in subduing him, Seefeld said.

Yakshe handcuffed the boy as police arrived at the school. Seefeld said the teen was treated for a minor hand wound.

Nate Moore, 15, was stabbed during the rampage and said he had to be treated with 15 stitches.

"It was really fast. It felt like he hit me with a wet rag because I felt the blood splash on my face. It spurted up on my forehead," Moore told the AP.

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At least 20 people were injured after the stabbings at the start of the school day, Westmoreland County emergency management spokesman Dan Stevens said.

The motive for the rampage remains under investigation. Seefeld said they were not aware of any warning signs from the suspect, a sophomore at the school.

At least four people with injuries emergency management officials described as "serious" were flown to area hospitals for treatment. Others were not actually stabbed, he said, and some of their injuries included cuts and scrapes.

Among the stabbing victims was a security guard stabbed in the stomach, the police chief said.

Dr. Louis Alarcon, who is part of an operating team at the University of Pittsburgh Medical Center Children's Hospital, said one victim, a 17-year-old boy, had a stab wound to the chest that barely missed his aorta.

At Forbes Hospital, Dr. Mark Rubino said his team treated eight victims, three of whom he said had severe injuries.

"We were ready to handle what came in the door," Rubino said, adding that, at one point, 20 surgeons were in the emergency room.

Rubino said the injuries spanned from "relatively superficial wounds" to "severe injuries to abdominal injuries." He said almost all of the stab wounds appeared to follow a pattern and were inflicted on the victims' lower abdomens.

The breakdown of injured and whether they were students or staff was not immediately known, but Forbes and Allegheny General Hospital initially reported nine patients ranging in age from 15 to 60.

A student, who said he knows the person believed to be the alleged stabber, said the teen -- described as skinny -- seemed like a "pretty normal kid."

Alyssa Finch, who said she is a student at Franklin Regional High School, told ABC News a fellow student pulled the fire alarm during the stabbing "because he knew what was happening ... and he wanted the people to get out."

Seefeld, the police chief, also credited the assistant principal who he said tackled the suspect -- identified by relatives and students as Sam King.

"I can tell you he is being looked at, though, but he was not stabbed," Seefeld said of the assistant principal.

Cole Seymour, a junior at the school, described the assistant principal as "the kind of faculty member that every student in the building could go to."

"He went out of his way to make students feel comfortable and see how they were," Seymour told ABC News.

As the community bands together after a horrific morning, Rubino said he has seen groups of students flocking to the hospital to visit their injured friends.

"Some of students I spoke to were glassy-eyed. They were somewhat teary-eyed. They described confusion of the moment and just the real concern that they had for friends," Rubino said. "Prom is coming up soon, and that should what's on their mind and it's not."